It is generally known that cam mechanisms are used to produce repetitive cycles of linear displacement. A particular application requiring linear displacement is the activation of a switch. A cam rotating in a first direction causes the switch to close thereby creating a short circuit. The cam rotating in a second direction, causes the switch to open thereby causing an open circuit.
A cam operated switch typically comprises a cam attached to a shaft and conventional push button, limited travel switch. A limited travel switch has a finite actuation distance and does not allow the switch plunger to continue traveling after switch contact has been made. The push button switch is typically wired or hand soldered to a printed circuit board such that the switch's open state or closed state is recognized by associated circuitry.
Significant problems arise when implementing the cam operated switch concept to very small switches, otherwise known as microswitches. One type of microswitch comprises a plunger which collapses a metal dome under pressure. The plunger and metal dome are enclosed within a switch housing. Typically, two terminals exit the switch housing for detecting an open or collapsed dome state.
Problems associated with microswitches include a short actuation travel distance and no capability for over travel. The sensitive actuation nature of the microswitch requires precise cam dimensions and precise positioning of the cam above the switch plunger. The cam must rotate from its first position to its second position causing the plunger to collapse the dome over a very short distance. Since the microswitch does not have the capability of over travel (further actuation of the plunger beyond the point after the switch makes contact), the cam must stop exerting force at the actuation distance otherwise damage to the switch may occur. Manufacturing tolerance buildup resulting form this cam operated switch produces a frequently unreliable mechanism. Tolerances affecting the mechanism include soldering the microswitch to a printed circuit board, positioning of the printed circuit board, manufacturing of the microswitch itself, manufacturing of the cam, rotation of the cam and positioning of the cam above the switch plunger.
Advances in microelectronic devices demand smaller, inexpensive and easily manufactured switching mechanisms which current standard microswitches do not fulfill. Therefore, there is a need for a reliable miniature switching mechanism responsive to rotational movement which overcomes the aforementioned unavoidable problems.